The disclosure of Japanese Patent Applications No. 2001-275520 filed on Sep. 11, 2001, including its specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a catalytic emission control apparatus and a control method for the emission control apparatus, that controls emission by using an emission control catalyst.
2. Description of the Related Art
Substances contained in exhaust gas from an internal combustion engine, such as nitrogen oxides NOx, carbon monoxide CO, hydrocarbons HC, etc., are removed or lessened by a three-way catalyst disposed in an exhaust passage. In diesel engines, a four-way catalyst for removing or lessening particulate matter in addition to the aforementioned substances is employed.
An emission control catalyst also has a property of absorbing and storing oxygen. Utilizing the oxygen storage function, an attempt has been made to further improve the removal rates of the aforementioned substances. The present inventors have conducted further researches for more effective emission control based on the oxygen absorption-storage action of an emission control catalyst, and have accomplished the invention. That is, it is an object of the invention to provide an internal combustion engine emission control apparatus and a control method for the emission control apparatus, capable of further improving the emission control performance of the emission control catalyst by utilizing the oxygen absorption-storage action of the emission control catalyst.
Furthermore, the inventors have accomplished an emission control apparatus capable of further improving the emission control performance in a hybrid vehicle, by focusing attention on the amount of a specific component let out of the emission control catalyst. That is, it is another object of the invention to provide an internal combustion engine emission control apparatus and a control method for the emission control apparatus, capable of further improving the emission control performance of the emission control catalyst based on the amount of the specific component in exhaust gas flowing out of the emission control catalyst.
A first aspect of the invention is an emission control apparatus of an internal combustion engine that has an engine stop mode of stopping an engine during a run of a vehicle, the emission control apparatus utilizing an oxygen absorption-storage action of an emission control catalyst disposed in an exhaust passage of the internal combustion engine. The emission control apparatus includes a storage computing device that computes a storage of oxygen in the emission control catalyst, and air-fuel ratio controller that performs an air-fuel ratio control of the internal combustion engine based on the storage of oxygen computed by the storage computing device. The storage computing device computes the storage of oxygen during the engine stop mode of the internal combustion engine. The air-fuel ratio controller performs the air-fuel ratio control when the engine is restarted after the engine stop mode is discontinued, based on the storage of oxygen computed by the storage computing device during the engine stop mode.
Examples of the vehicle that has the engine stop mode include generally termed hybrid vehicles that have an internal combustion engine and an electric motor as drive power sources, vehicles equipped with a generally termed idle stop system that stops the engine (prevents idling) when the vehicle stops at an intersection and the like, etc.
According to the first aspect, even during the engine stop mode, the storage of oxygen is computed, and the air-fuel ratio control following restart of the engine is performed based on the oxygen absorption-storage capability. Therefore, deterioration of the emission control performance immediately after restart of the engine can be prevented, so that the emission control performance can be further improved.
In the first aspect, the air-fuel ratio controller may determine a change in the air-fuel ratio within a predetermined time following a restart of the engine, based on the storage of oxygen computed by the storage computing device during the engine stop mode, when the air-fuel ratio control is performed at a time of a restart of the engine. Therefore, deterioration of the emission control performance can be further improved.
In accordance with a second aspect of the invention, an emission control apparatus of an internal combustion engine of a hybrid vehicle that is run via the internal combustion engine and an electric motor utilizes an emission control catalyst disposed in an exhaust passage of the internal combustion engine. The emission control apparatus includes an output distribution controller that controls a distribution between an output of the internal combustion engine and an output of the electric motor. The output distribution controller controls the distribution of output between the internal combustion engine and the electric motor based on a condition parameter of an exhaust system of the internal combustion engine.
In the second aspect, the emission control apparatus may include a storage computing device that computes a storage of oxygen in the emission control catalyst, and the output distribution controller may control the distribution of output between the internal combustion engine and the electric motor so that the storage of oxygen computed by the storage computing device is within a predetermined range.
According to the above aspect of the invention, by controlling the output distribution so that the storage of oxygen becomes within a predetermined range in a hybrid vehicle, the driving by the electric motor is effectively employed so as to further improve the emission control performance using the oxygen absorption-storage action without deterioration in the drivability of the vehicle.
In the above aspect, an air-fuel ratio feedback control based on an exhaust air-fuel ratio may be performed if the storage of oxygen computed by the storage computing device is within a predetermined range. Therefore, the emission control utilizing the oxygen absorption-storage action and the emission control based on the air-fuel ratio feedback control are made compatible with each other at a high level, so that the emission control can be effectively performed.
In the second aspect, the output distribution controller may control the distribution of output between the internal combustion engine and the electric motor so that an amount of a specific component in an exhaust gas that flows out of the emission control catalyst is within a predetermined range.
According to the above aspect, the output distribution is controlled in a hybrid vehicle so that the amount of the specific component in exhaust gas flowing out of the emission control catalyst is within the predetermined range. Therefore, the emission control performance can be further improved.
In the above aspect, if the amount of the specific component in the exhaust gas that flows out of the emission control catalyst is within the predetermined range, an air-fuel ratio feedback control based on an exhaust air-fuel ratio may be performed.
If the amount of the specific component in the exhaust gas that flows out of the emission control catalyst is within a predetermined range, a normal air-fuel ratio feedback control is performed on the internal combustion engine. Therefore, the emission control based on the control of the amount of the specific component and the emission control based on the air-fuel ratio feedback control are made compatible with each other at a high level. Hence, effective emission control can be accomplished.
In accordance with a third aspect of the invention, an emission control apparatus of an internal combustion engine of a hybrid vehicle that is run via the internal combustion engine and an electric motor utilizes an oxygen absorption-storage action of an emission control catalyst disposed in an exhaust passage of the internal combustion engine. The emission control apparatus includes an absorption-storage capability computing device that computes an oxygen absorption-storage capability of the emission control catalyst, and an output distribution controller that controls a distribution between an output of the internal combustion engine and an output of the electric motor. The absorption-storage capability computing device computes the oxygen absorption-storage capability by serially performing a fuel stop and a rich operation. At a time of computation of an oxygen absorption-storage capability by the absorption-storage capability computing device, the output distribution controller controls the distribution of output between the internal combustion engine and the electric motor so as to provide an output required of the vehicle.
According to the third aspect, the fuel stop and the rich operation are serially performed in the hybrid vehicle, so that the oxygen absorption-storage capability can be accurately detected at an earlier timing. Therefore, the emission control performance utilizing the oxygen absorption-storage action can be further improved.
In accordance with a fourth aspect of the invention, an emission control apparatus of an internal combustion engine of a hybrid vehicle that is run via the internal combustion engine and an electric motor utilizes an oxygen absorption-storage action of an emission control catalyst disposed in an exhaust passage of the internal combustion engine. The emission control apparatus includes an absorption-storage capability computing device that computes an oxygen absorption-storage capability of the emission control catalyst, and an output distribution control device that controls a distribution between an output of the internal combustion engine and an output of the electric motor. The absorption-storage capability computing device computes the oxygen absorption-storage capability by serially performing a lean operation and a rich operation near a limit within a maximum range of combustible air-fuel ratios. At a time of computation of an oxygen absorption-storage capability by the absorption-storage capability computing device, the output distribution controller controls the distribution of output between the internal combustion engine and the electric motor so as to provide an output required of the vehicle.
According to the fourth aspect of the invention, the lean operation and the rich operation are serially performed near the limit of combustible air-fuel ratios in the hybrid vehicle, so that the oxygen absorption-storage capability can be accurately detected at a early timing without deterioration of the drivability. Therefore, the oxygen absorption-storage capability based on the oxygen absorption-storage action can be further improved.